Olmesartan medoxomil, 4-(1-hydroxy-1-methylethyl)-2-propyl-1-[[2′-(1H-tetrazol-5-yl)[1,1′-biphenyl]-4-yl]methyl]-1H-imidazole-5-carboxylic acid has the formula as given below:

Olmesartan medoxomil is found to be an excellent Angiotensin II receptor antagonist activity and is therefore useful as antihypertensive drug and for the therapy and prophylaxis of heart diseases.
U.S. Pat. No. 5,616,599 discloses a process for the preparation of Olmesartan medoxomil comprising                Condensing the ethyl 4-(1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylate with 4-[2-(trityl tetrazol-5-yl)phenyl]benzyl bromide in presence of NaH/DMF to obtain ethyl 4-(1-hydroxy-1-methyl ethyl)-2-propyl-1-{4-[2-(trityl tetrazol-5-yl)phenyl]phenyl}methyl imidazole-5-carboxylate        Reacting the above; obtained compound with lithium hydroxide in dioxane to obtain corresponding lithium carboxylate, which is then reacted with 4-chloromethyl-5-methyl-2-oxo-1,3-dioxolene in presence of K2CO3/DMA and the obtained residue is subsequently crystallized from IPE to obtain trityl Olmesartan medoxomil, which is then deprotected in presence of acetic acid/water followed by crystallization in ethyl acetate to obtain Olmesartan medoxomil        
U.S. Pat. No. 5,744,612 discloses a process for producing Olmesartan and Olmesartan alkyl ester comprising the step of reacting ethyl ester of 1-(2′-cyanobiphenyl-4-yl)methyl-4-(1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylic acid with an inorganic azide such as sodium azide in an aromatic hydrocarbon solvent such as toluene or xylene in the presence of an amine salt such as triethylamine hydrochloride to obtain Olmesartan ethyl ester followed by hydrolysis to Obtain Olmesartan
The US'612 also discloses a process for preparing a 5-substituted tetrazole comprising the step of reacting a nitrile with an inorganic azide in aromatic hydrocarbon such as toluene or xylene in the presence of an amine salt such as triethylamine hydrochloride.
US 2005/0119488 claims the compounds containing cumyl tetrazolyl group or an isomer or tautomer thereof and claims a process for the deprotection of a compound containing cumyl tetrazolyl group by deprotecting the 4-(1-hydroxy-1-methylethyl)-2-propyl-1-{[4-2-(cumyltetrazol-5-yl)phenyl]phenyl}methylimidazole-5-carboxylic acid (cumyl Olmesartan) in presence of anhydrous HCl or HBr in an organic protic or aprotic solvents preferably MDC or EtOAc or toluene to produce 4-(1-hydroxy-1-methylethyl)-2-propyl-1-{[4′-tetrazol-5-yl)phenyl]phenyl}methyl imidazole-5-carboxylic acid (Olmesartan).
US 2006/0069141 discloses a process for the preparation of Olmesartan medoxomil in which trityl Olmesartan medoxomil is contacted with an acid in a mixture of water miscible organic solvent and water. Preferred water-miscible organic solvents include acetone, acetonitrile and t-butanol and most preferred solvent is acetone and water in about 1:3 to about 3:1 by volume. By the above process it is given that the impurity-Olmesartan acid is reduced to less than about 1% and the Olmesartan medoxomil is obtained directly without the evaporation step as given in the U.S. Pat. No. 5,616,599.
US 2006/00069141 discloses a process for preparing Olmesartan Medoxomil comprises                Contacting trityl Olmesartan medoxomil with an acid in a water miscible organic solvent, with or without water, to obtain a solution of Olmesartan medoxomil and a precipitate of triphenyl carbinol,        Separating the precipitate of triphenyl carbinol from the solution of Olmesartan medoxomil and contacting the solution of Olmesartan medoxomil with a base to obtain a precipitate of Olmesartan medoxomil.        
US 2006/00069141 also describes the drawbacks of the prior art methods wherein Olmesartan medoxomil is isolated from acidic conditions contains around 2.2% Olmesartan acid impurity by HPLC.
US 2006/0074117 discloses a process for purifying Olmesartan Medoxomil comprising:                contacting trityl Olmesartan medoxomil with an acid in a water-miscible organic solvent to obtain a solution of Olmesartan medoxomil and a precipitate of triphenyl carbinol,        separating the precipitate of triphenyl carbinol from the solution of Olmesartan medoxomil and contacting the solution of Olmesartan medoxomil with a base to obtain a precipitate of Olmesartan medoxomil.        recovering the precipitate of Olmesartan Medoxomil        dissolving the precipitate of Olmesartan Medoxomil in a C3-6 ketone and adding water to recover the purified Olmesartan Medoxomil.        